Automatic radio listener survey system



May 11, E954 w. D. HORN ETAL AUTOMATIC RADIO LISTENER SURVEY SYSTEMFiled Dec. 16, 1948.

5 Sheets-Sheet 1 Clttomeg May 11, 1954 w. D. HORN ETAL AUTOMATIC RADIOLISTENER SURVEY SYSTEM Filed Deo. 16, 1948 5 Sheets-Sheet 2 Rig Umm.

May `11, E954A W. D. HORN rl-:T AL 2,678,382

AUTOMATIC RADIO LISTENER SURVEY SYSTEM Filed Dec. 16, 1948 5Sheets-Sheet 3 nnentors n//LL/AM D. HORN. .7b4/v hf. ,SAGA ZZ//V/Gttorneg Patented May 11, 1954 AUTOMATIC RADIO LISTENER SURVEY SYSTEMyWilliam D. Horn and John R. Ragazzini, New York, N. Y.; said Ragazziniassignor to said Horn Application December 16, 1948, Serial No. 65,596

(Cl. Z50-2) Claims.

This invention relates to an automatic radio listener survey system andmore particularly to a system for making an automatic record of thenumber of home radio receivers in a selected group which are tuned to agiven radio broadcast at any given time.

An object of the invention is to provide a system of the above typewhich records suicient data to permit the records to be broken down andtabulated in accordance with the different types of information desired,for example, according to areas, according to income groups, accordingto selected intervals, etc.

Another object is to provide a system of the above type in which theinformation from scatu tered communities may be readily assembled andanalyzed at a given central point.

Another object is to provide a system of the above type which does notrequire the aid of special signals from the broadcast station and,consequently, dies not require the cooperation of the broadcast company.

Another object is to provide a system of the above type which operatesin response to a selected normal recurring characteristic of thereceived program.

Various other objects and advantages Wil1 be apparent as the nature ofthe invention is more fully disclosed.

In accordance with the present invention, the control is eiiected inresponse to a recurring normal characteristic of the received programwhich may comprise, for example, a selected audio frequency note orseries of notes, or a selected audio volume level. in a specicembodiment the silent ieriods in the audio frequency are utilized forthe controls. Such silent periods may, for eX- ample, constitute theintervals between Words or syllables of a spoken program or the rests ina musical program. Such periods normally have a duration of only afraction of a second and recur on an average of more than oncepersecond. The time distribution of such silent periods constitutes acode which is distinctive for each received program.

More specically, a central recording station is connected to each of theselected home receivers by a conductor, such as a telephone line, or atransmission link, such as a radio beam. The audio signal being receivedby the home receiver is imposed on this line by suitable means, such asa microphone placed in the radio receiver, or by a suitable connectionto the audio frequency output circuit of the receiver. At the centralrecording station this audio signal is applied to a signal generatorwhich is adapted to produce a signal of a distinctive frequencymodulated or controlled by the received audio signal in such a mannerthat the local signal is generated only during the non-silent periods ofthe received audio signal. A plurality of monitoringreceivers are alsodisposed at the central recording station, one for each of the broadcaststations for which data is required. The audio frequency output of eachof the monitor receivers is supplied to a local signal generator similarto that actuated by the home receiver, but each generator has adistinctive tone of frequency which is preferably in the audio'frequency range although higher frequencies may be employed if desired.

For comparison purposes a time signal is also received at the centralstation. This may be a radio time signal or a Western Union time signaloperating to produce a tone pulse on each hour. The time sig-nalactuates a further signal generator producing its own distinctive tone.

The various tones thus produced are passed through a suitable amplierand applied to a recording head operating on a suitable recordingmedium, such as a disc record which is driven at a speed such that therecording period may cover a full days listening or at least the periodof the day during which the data is to be obtained. The record groovethus carries the tones corresponding to the time signal, the variousbroadcast prog-rams, and a particular home receiver which is to beanalyzed. A separate record of this type is made for each of the homereceivers and suitably marked for identication so that the records maybe grouped as desired for analysis.

The records are analyzed automatically at a master decoding stationwhich may be located at the central recording station above referred to,or may be located at another suitably selected point in which all of therecords from the various recording stations are assembled.

At the master decoding station the records are automatically analyzed,the programs to which the listener was tuned at various time periods aredetermined, and selected counters are actuated which automaticallyregister the total number of receivers tuned to each of the selectedprograms at each selected time period.

This is accomplished at the master decoding station by playing back eachrecord through a lter circuit having means for separating the varioustones which are recorded thereon. Each of the tones is then applied to apulse former which is adapted tov produce a pulse of short duration andgiven amplitude at the onset of each silent period of the tone beingmeasured. The pulses from the tone representing the home receiver arethen compared in separate trigger circuits with the pulses derived fromeach of the monitors. The trigger circuits operate gate circuits whichare arranged to produce pulses of a predetermined duration suited toactuate relays controlling the counters. A pair of gate circuits may beactuated by each of the trigger circuits, one gate circuit producingpulses when there is coincidence between the pulses supplied to thetrigger circuits and the other gate circuit producing pulses when thereis lack of coincidence in the pulses applied to the trigger circuit. Thepulses from each of the rst gate circuits constitute stepping pulseswhich are connected to actuate a stepping relay and the pulses from eachof the second gate circuits constitute release pulses which are adaptedto return the relay to its initial position. The relay in each channelaccordingly advances step-by-step as long as there is coincidencebetween the initial pulses and is restored to its starting position assoon as any lack of coincidence occurs. After a relay has advanced apredetermined number of steps which are selected to reduce thepossibility of spurious operation, a circuit leading through a slowacting relay is closed and will remain closed until the stepping relayis restored to its initial position, that is the circuit to the slowacting relay remains closed as long as there is coincidence between thepulses, indicating that the home receiver is tuned to the designatedradio broadcast program.

The relay itself remains closed as long as the home radio is on. Whenthe signal from the home radio is off for 30 seconds or more the slowacting relay breaks the circuit. This is necessary because of thepossibility that some home radio might be tuned to a radio station whenthe station goes off the air. In such a case, the slow acting relay willbreak the circuit and the counter will stop.

When there is coincidence between the pulses from the home radio and themonitor, the stepping relay will operate one of a bank of counters toindicate that the home radio being analyzed is listening to station A atthe time interval represented by the counter. It is to be understoodthat a set of trigger circuits, gate circuits, stepping relays, timedrelays and counters will be provided for each of the stations beingmonitored.

In order to determine the time distribution of the listening habits,each bank of counters represents one radio station or radio network andcontains a number of counters representing the various time periods intowhich the home radio listening analysis is to be broken down and may, ifdesired, constitute separate counters for each minute of the day, inwhich event the counters are connected to a selector switch which isactuated by a time signal to step the switch from one counter to thenext one each minute. In this way the number and distribution of thecounters actuated indicates the time periods during which the listenerwas tuned to the respective station.

The above procedure is repeated for each of the records at the masterdecoding station. When all of a group of records have been played back,the counters then designate the number of home receivers tuned to eachof the selected programs during each selected time period. An additionalbank of counters may also be provided to be actuated when an audiosignal is received on any of the home receivers. This additional bank ofcounters will thus record tnc total number of receivers in operation atany particular time.

In order to reduce the time required for analysis the records may beplayed back at a speed several times their original speed during 'therecording period, the timing of the various circuits being alteredaccordingly, or if desired a plurality of the records may be played inoverlapping sequence by duplicating for each record in the plurality theequipment up to the baril: of counters, in which case it is necessary todisplace the records in time so that no two records are connected to thesame counter at the saine time.

The nature of the invention will be better understood by referring tothe following description, taken in connection with the followingdrawings in which a specific embodiment thereof has been set forth forpurposes of illustration.

In the drawings:

Fig. 1 is a schematic diagram illustrating the system at the homereceiver and at the central recording station for recording the varioussignals;

Fig. 2 is a similar schematic block diagram illustrating the equipmentat the master decoding station for analyzing the data on the records;

Fig. 3 is a schematic diagram of a signal generator used in the systemof Fig. l;

Fig. 4 is a schematic diagram illustrating one type of pulse-formingcircuit for use in the system of Fig. 2;

Fig. 5 is a schematic diagram illustrating one type of trigger circuit;and

Fig. 6 is a schematic diagram illustrating a type of gate circuit.

Referring rst to Fig. l, the system is shown as utilized for analyzingthe programs received by a home receiver i@ which is adapted to receivea program of the type being analyzed, for example, a radio broadcastprogram, television program, facsimile, or the like. The home receiverincludes the usual audio circuit which is connected through an amplifierl! so as to avoid interference with the received program, to atransmission line I2 which may constitute a telephone line, power line,or radio link connecting the home receiver with the central recordingstation.

The central recording station includes a plurality of monitor receiversl5, two of which are shown for convenience and are assumed to be tunedto broadcast programs A and B which are to be analyzed. It is to beunderstood that the number of monitors l5 will correspond to the numberof programs which are to be received and analyzed simultaneously. A timesignal is supplied by a line I6 which may comprise a Western Unionsignal or a radio time signal.

The line l2 at the central recording station is connected to a controlsignal generator El which is adapted to generate a tone of a frequencyfr. The signal generator is such that the tone f1- is supplied to a linei8 during the non-silent periods of the received program.

The monitor receivers l5 are likewise connected. to signal generators I9each of which is adapted to generate and supply a distinctive tone atfrequencies fa and fb to lines 20a and 2Gb respectively during thenon-silent periods of the respective received monitored programs. Thetime signal from the line I6 is supplied to a similar signal generatorgtwhich is adapted to produce a distinctive tone of frequency ft andsupply the saine to a line 261i at intervals corresponding to the timesignal or, if the time signal itself constitutes a distinctive tone, thesignal generator ist may be omitted.

The lines 2da, Zlib and 2st are suppiied to a suitable amplifier 2|Where the signals are cornbined with the signal from the signalgenerator I'i and are fed to a recording head 22 where they are recordedon a record 23 which has been indicated as a disc record, but mayconstitute any suitable recording medium and is driven at a speed suchthat a whole days program may be recorded on a single record.

It is to be understood that each home receiver i@ Will be connected to aseparate signal gen'- erator and amplier and its signals will berecorded on a different record. The lines Zta, 2th and Eiit may,however, be common to the various amplifiers so that only one set ofmonitor receivers and signal generators are required. The tone from eachgenerator ifi is of course of a different and distinctive frequencydesignated as fc, fb, etc.

It is to be understood that signal generator il may be incorporated inthe home receiver instead of at the central recording station ifdesired, in which case the tone ,fr will be applied to the line i2 atthe designated home and `will be transmitted by the line l2 to thecentral recording station. rhis may be preferable in certain instances,as for example where several receivers are located the same home, inwhich case the signal genrator may generate a different signal frequencyfor each of the home receivers and apply the various frequencies to thesame line i2. All of the frequencies representing the differentreceivrnay thus be recorded on the saine record 2t. Similarly, a groupof frequencies representing receivers in a selected group of homes maybe applied to the same line i2 and may be recorded on the saine record23 thereby eliminating certain duplications of apparatus at the centralrecording station and also permitting the data from a plurality ofreceivers to be analyzed at the same time in the master decodingstation.

The signal generator l'i, i9 and Hit may be of the type shown in Fig. 3.In Fig. 3 the leads iii carry a signal which may be the audio signalfrom any of the receivers It or monitors i5 of Fig. l to primary 4i oftransformer 42 having a secondary i3 connected through a resistor 44 toa rectifier tube 45 and a resistor i5 in series circuit. A condenser 4lis connected across the resistor Kit. During periods of audio frequencyoutput from the secondary d3, a rectified current passes through theresistor 46 in the direction of the arrow, producing a voltage dropthereacross. The negative end of the resistor it is connected through abiasing battery iii! to ground at d. The battery di! is connected tosupply a negative bias with respect to ground to the resistor 4S. Alimiter tube tu with a biasing battery 5i is ccnnected across the tube45 and resistor -ii to limit the voltage drop produced across theresistor 136.

The positive end of the resistor @it is connected by a lead 52 andresistor 53 to the control grid 54 of an amplifier tube 55. Theconnections are such that with a normal audio frequency output from thesecondarylis, the voltage drop across the resistor 6 produces a positivebias with respect to ground VWhich is suincient to make tube 55operative. However, during silent periods, the

battery 48 supplies a negative bias through the line 52 to the controlgrid 54 which causes the tube 55 to be cut oli. The tube 55 accordinglyfunctions only during the non-silent periods.

The control grid 5d is also supplied with an alternating voltage from anoscillator 56 which is connected through a lead 5'? and condenser 58 tothe grid 54. The oscillator t may be of any standard type adapted tooperate continuously to produce a continuous signal of characteristicfrequency and to supply the same to the control grid 5ft. The A. C.signal, however, is amplified by the tube 55 only during the non-silentperiods when a positive bias is superimposed on the negative biassupplied to the control grid from the battery d8.

The tube 5@ and biasing battery 5l constitute a limiter to prevent thepositive bias supplied to the line 52 from becoming excessive. if thebattery 5i is of the same potential as the battery 48, then thepotential drop across the resistor 4t will combine With the bias acrosscathode resistor 59, the battery 43, and resistor to cause tube '55 tobe in a normal operating condition produced by its own bias resistor 5t.In that event the bias on the grid it Would vary from the negativecut-off value of the battery 48 to normal operating value.

The tube is shown as provided with a cathode Se which is connectedthrough resistor '.99 and condenser Si to ground at (i2, and with ascreen grid 63 which is connected through a resistor 64, ley-passed bycondenser $5, to a source of positive biasing potential. A suppressorgrid E6 is connected to the cathode 653. An anode 61 is connected by anoutput lead 68 and a resistor 69 to a source of positive platepotential.

The arrangement is such that during non-silent periods an A. C'. voltageof characteristic frequency, such as fa, fb, fr, or fr, from theoscillator 5t appears in the lead t3, but during silent periods with noaudio frequency output from the receivers, the tube 55 is blocked and nosignal appears on the lead 68.

t is understood, therefore, that during periods of program silence, nosignal will appear on the leaded. However, during periods of programnon-silence, a signal of characteristic frequency fa, fb, or fr willappear on the line 63 which corresponds to the lines I B, 2Enl or 20o ofl. Similarly, during each time signal, a signal of characteristicfrequency ft will appear on the line B8 which corresponds to line Zet ofFig. l.

Referring now to the master decoding station shown in Fig. 2, the record23 containing the various tone recordings is driven either at the sainespeed as in Fig. l or at a higher rate of speed and the recordings arepicked up from a pick-up head 'F5 and supplied by a line 'is to a-filter circuit 'il which may be of any desired type adapted to separatethe different tones and may comprise a set of multi-channel amplifierseachof which may be in the form of a feed-back amplifier which is tunedto a particular characteris'tic frequency. The tone of frequency fa, fb,fr and ft are thus segregated and supplied by suitable leads to pulseformers Tic, Tib, Tir, Tt, respectively. These pulse formers, which maybe of the type shown in Fig. 4, are adapted to produce a short, ilattopped pulse of constant amplitude at the onset of a silent period inthe tone fa, fb, etc. to which the respective pulse formers areresponsive.

The pulses from the pulse formers Tiuand 'iib are supplied by lines 18aand 'hib to trigger cir- `cuits iSd and 'i919 respectively. The pulsesfrom the pulse former circuit 111' are supplied by a line 181' to bothtrigger circuits 19al and 19h. The trigger circuits may be of the typeshown in Fig. 5 and are adapted to produce a response in output lines80a and Sill) respectively when the input pulses of the respective line18a or 18h are coincident with the pulses in the line 181. Theseresponses are supplied by the lines 80a and 89h to gate circuits 81a andSib respectively. These gate circuits may be of the type shown in Fig. 6and are adapted to produce an output pulse of given duration in responseto an input signal in the lines 80a or 8011.

The trigger circuits 19a. and 19h are also adapted to produce a responsein lines 82a and 82o respectively when there is non-coincidence betweenthe pulses supplied to the respective trigger circuits from the line181` and the line 18a or 1817. These responses in the lines 82a and 82hare supplied by the gate circuits 83a and 83h respectively which may besimilar to the gate circuits la and lb above referred to.

The channel corresponding to the station A is provided with a steppingrelay 84a. This stepping relay is of any suitable type and is indicatedas provided with a plurality of contacts 85a which are successivelyengaged by arm 85a in response to successive energization of a steppingcoil 81a. The relay is of the type in which the arm 85a is automaticallyrestored to its initial position in response to actuation of releasecoil 88a.

The gate circuit Sla is connected to stepping coil 81a and the gatecircuit 83a is connected to release coil 88a so that each pulse from thegate circuit 81a, corresponding to coincidence in the input pulses,results in stepping the relay 813:1. around one position, and each pulsefrom the gate circuit 83a, corresponding to non-coincidence, results inrestoringr the relay to its initial position.

One of the contacts of the stepping relay, shown as the fourth contact,is connected through the armature 95a and contact 91a of a slow actingrelay 96a to the arm ia of a stepping relay lilla which is of a typehaving a large number of contacts which are closed in succession inresponse to successive actuations of a stepping coil H2201. The contactsare individually connected to banks of counters 10511.

The frequency ft, corresponding to the time signal, is applied to apulse former 111*J to produce time pulses which are supplied by line181i t a time pulse former 106 which produces pulses of a short durationat timed intervals. The time pulse former produces pulses which operatethe stepping relay la. The time pulse former produces, for example,sixty pulses between successive time signals on the record. The timesignals on the record may appear once each hour as recorded at thecentral recording station. Each time signal on a record causes the timepulse former to correct itself if it is not precisely coordinated withthe time signal in a manner similar to a standard Western Unionelectrically-controlled clock. The time pulse former 06 is connected bya line 01 and line |08 to the stepping coil I02a of the stepping relaymia.

The lead carrying the signal fr is also connected by a lead 98 to adetector and rectier 95 which is adapted to supply an output currentwhenever a signal fr appears without extended interruptions which wouldcorrespond to the home radio being tuned off. This output current issupplied by a line ID3 to the coil of the relay 96a and is adapted tohold the contact 91a closed whenever the home radio is tuned to anyprogram, but to open the contact 91a after a predetermined period suchas 30 seconds and thereby stop the counters |05a from operating when noprogram is being received by the home radio. The stepping relays,counters and associated circuits in channel B are supplied in a similarmanner from the output of gate circuits 8 lb and 3319 and have beengiven similar reference characters with the suix b. It is to beunderstood that similar channels and counters will be provided for eachof the programs being analyzed.

The lead |03 is also connected to coil 961 of a slow acting relay havingan armature 951" engaging a contact 911- which is connected to the arm|1101' of a stepping relay ||1- having a group of contacts connectedrespectively to counters |051'. The stepping relay wir is provided witha stepping coil |021 which is connected to the line |01.

In the operation of the system shown in Fig. 2, the various tones fa,fb, fr, fr, etc., derived from the record 23, are separated in thefilter circuit 11 and individually supplied to pulse former 11a, 11b,111* and 11i, respectively. Considering the circuit constituting channelA, the pulses from the former 11a and 111' are supplied to the triggercircuit 19a wherein the pulses are compared and when the pulses arecoincidental, signals are supplied through the line a to the gatecircuit Sla which produces a pulse to actuate the stepping coil 81a ofthe stepping relay 84a. When four successive pulses have been received,the arm 86a will be stepped around to the fourth contact and therebyclose the circuit to the stepping relay lilla through slow acting relay96a. If, however, before four successive coincidental pulses arereceived a non-coincidence appears between the pulses from the formers11a and 111", a signal will be produced by the trigger circuit 19a inthe line 82a and supplied to the gate circuit 83a to produce a pulsetherein which actuates the release coil 88a and restores the arm 86a toits original position.

In the embodiment shown, the four successive coincidental pulses arerequired to produce a response in the timed relay in order to avoid thepossibility of spurious operations due for example to the accidentalcoincidence of said pulses when a receiver is tuned to a diiierentstation. The likelihood of receiving four successive coincidental pulseswithout a non-coincidental pulse except when the received and monitoredprograms match is extremely remote. Of course, more or less than thefour steps may be provided in accordance with the accuracy required.

A succession of four coincidental pulses is taken as an indication thatthe receiver was tuned to the broadcast station A and the coincidentalpulses will continue as long as the receiver is tuned to that station.However, after the stepping relay has reached the position four, nofurther movement thereof will take place and the circuit through slowacting relay 96a will remain closed until a non-coincidental pulse isreceived which actuates the trigger circuit 33a and produces a pulse toenergize the release coil 38d and restore the stepping relay to itsinitial position. Such a non-coincidental pulse indicates that thereceiver was no longer tuned to station A.

When arm 86a of stepping relay 84a reaches the fourth contact, it causesthe connected counter |05a to register. The stepping relay I0 Ia isactuated by the stepping coil |02a each time a pulse is received fromthe time pulse former |06. If the time signals are received once eachminute for example the stepping relay |Ia will be actuated each minuteto connect a different counter ||la into the circuit. With arm 86a onits fourth contact 85a each counter will count once when stepping switchIliIal connects it. This count will indicate that one home radio Wastuned to station A during the minute which the counter represents.

It is to be understood that the record 23 may be played back. at a speedgreater than that at which it was recorded, in which event, theswitching from one counter to the next Will be proportionally faster,but each counter 35a will still represent one minute of listening time.Obviously, this period may be varied as desired and a period of oneminute has been selected for reference purposes only.

It is to be understood, of course, that ir" the code of the frequency frderived from the record 23 corresponds to the code of the frequency fbderived from station B the stepping relay Stb would be actuated insteadof the relay 84a and the corresponding counters IEb would be actuated.

As long as a tone of the frequency fr appears on the record 23,indicating that the receiver is tuned to some program, the detector andrectiiier 99 produces pulses to actuate slow acting relay 961', which issimilar to the relay 96a, rerei-red to above, and is adapted to actuatecounters |5351'. The counters |651 are connected in sequence by steppingrelay IIlIi` which is also actuated by a stepping coil I 02T in responseto the time signal from the line IGT. Hence the counters I'n areactuated upon the appearance or a signal of the frequency fr regardlessof the station to which the receiver may have been tuned.

After each record has been played as indicated above, the steppingrelays IIlIa and lilIb, iillr,

etc. are restored to their initial positions and a second record isanalyzed. The second record covering the same radio broadcast day butfor a dierent home radio will then actuate the counters ia, i051), |051'in the same timed sequence as the rst record. This is repeated until allof the records in a group have been analyzed. The counter |05a. willthen individually register the total number of receivers which weretuned to station A during the various minutes represented by theindividual counters, the counters ib will show the number of receiverstuned to station B during the various minutes of the day represented bythe individual counters, and the counters I 05T will represent the totalnumber of receivers in use during the various minutes of the day. Bysubtracting from the total number of receivers in use the number of setstuned to station A, station B, and other stations for which there arecounters, one may obtain the number of sets tuned to those stations notrepresented by counters, which may be designated as all others.

The stepping relays IUI a, etc. may be of any standard type, such asthat commonly used in telephone circuits, for selecting a large numberof circuits and it is to be understood that the representation is onlydiagrammatic.

If the record 23 carries a plurality of tones representing severaldifferent receivers, the circuits designated With the sufx 1" will berepeated for each tone which is being analyzed and each tone may beanalyzed separately by suitable selection in the filter circuit TI, orthey may be analyzed simultaneously by duplicating the various analyzingcircuits. As pointed out above, a plurality of records may be analyzedsimultaneously by duplicating the various circuits shown in Fig. 2 withthe exception of the counters and so timing the reproducing of thedifferent records that no two records will be connected to the samecounter at the same time. In the embodiment shown, for example, thesecond record could start one minute after the start of the rst recordand the third record could start one minute after the start of thesecond record, and so on. While this would require duplication ofapparatus, it would materially reduce the time required to analyze therecords.

The pulse formers lla, 1lb, 17T and llt may be of the type shown indetail in Fig. 4. Referring to this iigure more in detail the signal ofcharacteristic frequency is applied from the line i2@ through condenser|2| to diode |22. This diode rectiles the signal so that when anon-silent period occurs on the program, a D. C. voltage appears acrossa resistor |23. A condenser ifi filters out ripple voltages which mayinterfere with the operation of the remainder of the circuit. Thecombination of condenser |25 and resistor |26 serves as adifferentiating circuit whose output is a negative pulse at the onset ofa silent period in the signal on the line |26 and a positive pulse atthe termination of a silent period. The positive pulses areshort-oircuited and thus removed by diode |21. Thus, only negativepulses which mark the onset of a silence appear on output line 8.

The trigger circuit 'i9 may be of the type shown in Fig. 5. In this gurethe line lim carrying the pulse derived from the pulse former 'lia isconnected to resistance |28 which is connected to a trigger and limiter|39 which is adapted to produce an output of a predetermined value whenrendered operative by a suitable impulse. The pulse from the line l8r isalso supplied through resistance |29 and line |3| to the input of thetrigger and limiter |30.

The trigger and limiter circuit |30 may include a tube having a grid |32and cathode Ii which is normally biased to a predetermined point belowcut-off by a battery |33 connected to ground.

Assuming the pulses supplied to the lines iSd and l8r to have anamplitude represented by unity, then the tube will be biased beyondcut-oir by the battery |33 by an amount represented by -l. In this caseit is evident that a pulse of amplitude -l-l received from either theline l8r/z or the line l8r will change the bias from l to 0, which isnot sufcient to pass the cut-oir point; hence no current will be passedby the tube. If the pulses on the lines 'ISa and 78T are coincidental,however, they will have a total value of |2 which superimposed upon thebias of -1 produced by the battery |33 will produce a positive bias ofthe value of +1 which will render the tube operative and allow the sameto pass a predetermined current. The trigger and limiter circuits areconnected to supply a positive pulse to the line |35 and to supply anegative pulse to the line I3?. The positive pulse may be of anypredetermined value. The negative pulse however is preferably of a value-2 and is supplied through a resistor |38 to a line E39 which 11 isconnected to the lead l8r and to ground through a resistor |40.

When no signal appears on either the line 18a or the line 'l8r no signalwill appear on the output line |39. If the pulses appear simultaneouslyon the lines 78a, and |81 and are each of a value of unity, as aboveassumed, the point receives a pulse of a value of +2 from the combinedpulses on the lines 78a and 181-. However, it also receives a pulse of avalue of -2 through the line |31 and resistor |38. Hence, a voltage willappear on the output line |39. In the event, however, that a pulse isreceived on either the line 'i3d or |81, but not on both lines, thepoint |4| will take a Value of -{-1 due to the input pulse, and sincethere is no output from the trigger circuit |30 at that instant, theline |39 will carry a pulse of a value of +1. Hence a pulse will appearon the line |39 whenever a pulse appears on either the line 18a or theline l8r, but not on both lines. A pulse on the line |39 accordinglyrepresents noncoincidence in the received pulses; whereas a pulse on theline |36 represents a coincidence.

A type of gate circuit for producing the pulses of predeterminedduration is shown in Fig. 6. This circuit consists of tubes |55 and |5|connected to transform a short input pulse into a positive output pulseof predetermined duration.

The input lead |52 is connected to the control grid |53 of the tube |5uand through a condenser |54 to the anode |55 of the tube |5|. The anodes|56 and |55 are connected through resistors |57 and |58 respectively toa source of positive plate potential. The tubes |50 and |5| are providedwith cathodes |59 and |66 respectively which are grounded at |6| and areconnected through a biasing battery |52, lead |63 and resistor |54 tothe control grid |65 of tube |5|. Grid |65 is also connected through aresistor |51 to a lead |69 and to the anode |55 of tube |55.

The tubes |53 and |5| are connected to produce an output pulse in thelead |59, the duration of which is independent of the duration of theinput pulse on the lead |52. The tube |55 is normally conducting and thetube is normally nonconducting. Upon the application of a negative pulseto the grid |53, the tube |50 becomes nonconducting and the tube l5!becomes conducting. When the tube |50 becomes non-conducting thepotential of the plate |56 rises, due to the removal of the voltage dropthrough the resistor |57. Hence a positive pulse is applied to lead |59.When the tube |5| becomes conducting, the bias voltage of the tubes areafected so as to cause the tube Iii to again become conducting and thetube |5| to become non-conducting. The period required for this cycledepends upon the circuit constants and is independent of the duration ofthe negative signal supplied by the input lead |52. Hence a positive D.C. pulse of timed duration is produced in the output lead |69 regardlessof the length of the input pulse.

It is to be understood that these circuits are representative only andthat the various circuits may be modified as desired. It is also to beunderstood that in Figs. 1 and 2 the return circuits and sources ofpotential for operating the various devices have been omitted forpurposes of simpliiication. Various changes and modifications may bemade therein as will be readily apparent to a person skilled in the art.

What is claimed is:

1. The method of determining whether a remote radio receiver which istunable to any one of a plurality of different radio broadcast programsis tuned to a selected one of said programs, which comprises derivingfrom the remote receiver a time sequence based on the recurrence ofperiods of predetermined instantaneous signal intensity of the signalsof the program being received thereby, monitoring said diierent programsby individual monitor receivers independently of said remote receiver,simultaneously deriving from the monitor receivers a time sequence basedon the recurrence of periods of the same instantaneous signal intensityof the signals being received by the respective monitor receivers, oneof which coincides with the rst mentioned time sequence, producing aseries of audio tones of different frequencies corresponding in numberto the remote receiver and to the various monitor receivers, modulatingone of said tones to recur in the time sequence derived from said remotereceiver, modulating the others of said tones to recur respectively inthe time sequences derived from said monitor receivers, and transmittingsaid audio tones recurring in said times sequences to a common receivinglocation.

2. A radio listener survey system for determining Whether a remote radioreceiver which is tunable to any one of a plurality of different radiobroadcast programs is tuned to a selected one of said programs, whichcomprises a signal generator generating a xed audio tone, meansresponsive to the output of said remote receiver to derive a timesequence based on the recurrence of periods of a predeterminedinstantaneous signal intensity of the signals appearing in said outputand to actuate said signal generator to produce a distinctive audio tonewhich recurs in said time sequence, a plurality of monitor receiverstuned respectively to said different radio broadcast programs, a signalgenerator for each of said monitor receivers, each of said lastgenerators generating a different audio tone, means responsive to theoutput of each monitor receiver to derive a time sequence based on therecurrence of periods of the same predetermined instantaneous signalintensity of the signals appearing in the outputs of the respectivemonitor receivers, one of which coincides with the rst mentioned timesequence, and to actuate the respective last mentioned signal generatorsto produce a series of distinctive tones which recur in the respectivetime sequences derived from said monitor receivers, and meanstransmitting said recurring audio tones from said generators to a commonreceiving location.

3. A radio listener survey system for determining whether a remote radioreceiver which is tunable to any one of a plurality oi diiierent radiobroadcast programs is tuned to a selected one of said programs, whichcomprises a signal generator generating a fixed audio tone, meansresponsive to the output of said remote receiver to derive a timesequence based on the recur-- rence of instantaneous non-silent periodsin the signals appearing in said output and to actuate said signalgenerator to produce a distinctive audio tone which recurs in said timesequence, a plurality of monitor receivers tuned respectively to saiddifferent radio broadcast programs, a signal generator 'for each of saidmonitor receivers, each of said last generators generating a differentaudio tone, and means responsive to the output of each monitor receiverto derive a time sequence based on the recurrence of instantaneousnon-silent periods in the signals appearing in the outputs of therespective monitor receivers, one of which coincides with the firstmentioned time sequence, and to actuate the respective last mentionedsignal generators to produce a series of distinctive audio tones Whichrecur in the respective time sequences derived from said monitorreceivers, and means transmitting said recurring audio tones from saidgenerators to a common receiving location.

4. The method of determining Whether a remote radio receiver which istunable to any one of a plurality of diierent radio broadcast programsis tuned to a selected one of said programs, which comprises derivingfrom the remote receiver a time sequence based on the recurrence ofperiods of predetermined instantaneous signal intensity of the signalsof the program being received thereby, monitoring said differentprograms by individual monitor receivers independently of said remotereceiver, simultaneously deriving from the monitor receivers a timesequence based on the recurrence of periods of the same instantaneoussignal intensity of the signals being received by the respective monitorreceivers, one of which coincides with the rst mentioned time sequence,producing a series of audio tones of different frequencies correspondingin number to the remote receiver and to the various monitor receivers,modulating one of said tones to recur in the time sequence derived fromsaid remote receiver, modulating the others of said tones to recurrespectively in the time sequences derived from said monitor receivers,and transmitting said audio tones recurring in said time sequences to acommon recording medium through which the time sequences of said rstmentioned audio tone can be compared with the time sequences of each ofsaid last mentioned audio tones to determine the time coincidence orlack of time coincidence thereof.

5. A radio listener survey system for deter mining whether a remoteradio receiver which is tunable to any one of a plurality of diierentradio broadcast programs is tuned to a selected one of said programs,which comprises a signal generator generating a xed audio tone, meansresponsive to the output of said remote receiver to derive a timesequence based on the recurrence of periods of a predeterminedinstantaneous signal intensity of the signals appearing in said outputand to actuate said signal generator to produce a distinctive audio tonewhich recurs in said time sequence, a plurality of monitor receiverstuned respectively to said diierent radio broadcast programs, a signalgenerator for each of said monitor receivers, each of said lastgenerators generating a different audio tone, means responsive to theoutput of each monitor receiver to derive a time sequence based on therecurrence of periods of the same predetermined instantaneous signalintensity of the signals appearing in the outputs of the respectivemonitor receivers, one of which coincides With the rst mentioned timesequence, and to actuate the respective last mentioned signal generatorsto produce a series of distinctive tones which recur in the respectivetime sequences derived from said monitor receivers, and meanstransmitting said recurring audio tones from said generators to a commonrecording medium through which they can be compared.

References Cited in the le of this patent UNITED STATES PATENTS NumberName Date 1,934,879 Potter Nov. 14, 1933 2,031,605 Jenkins et al. Feb.25, 1936 2,176,742 La Pierre Oct. 17, 1939 2,188,165 Thomas Jan. 23,1940 2,206,702 La Pierre July 2, 1940 2,213,886 Potter Sept. 3, 19402,354,336 Rusch Aug. 1, 1944 2,413,965 Goldsmith Jan. 7, 1947 2,427,670Goldsmith Sept. 23, 1947 2,439,201 Clark, Jr. Apr. 6, 1948 2,484,733Rahmel et al. Oct. 11, 1949 2,484,734 Rahmel Oct. 11, 1949 2,500,935Deitz Mar. 21, 1950 2,558,754 Horn et al July 3, 1951

